In 1980 the main thrust of our work will be in two directions. Firstly, we will attempt to answer several questions raised by our characterization of muscarinic excitation. Where are the muscarinic receptors located on the cell surface? This can be answered by iontophoretic mapping and autoradiography. Where are the M channels located? If they are not contiguous, is an intracellular messenger involved? This will be answered by internally perfusing the cells with a suction pipette. Also, we will ascertain whether our proposed mechanism holds for central neurons, using a single electrode clamp in a slice preparation. Secondly, we will characterize the biophysics and pharmacology of calcium currents in these cells. We will pay particular attention to their kinetics of activation and inactivation.